1. Field of the Invention
The present invention relates to a method for the examination of objects with ultrasound for which a spatial region of the object is scanned by using a 3D ultrasound probe and for which from the reflected echo-signals only those signals are selected which fulfill selectable requirements and are used to generate an image on at least one display according to the spatial position in which the echo is reflected.
2. Description of the Prior Art
Scanning a spatial region of an object and storing the echo information on an address which corresponds to the geometrically correct position is known (AT 358 155 B). For this purpose, a scan plane (B-mode or C-mode) is moved over the object which has to be examined. This scan is done either manually (together with a simultaneous detection of the position of the plane to a reference position) or by using a specialized 3D probe which does the movement of the scan-plane in an automated way (e.g. AT 1708 GM). This volume-scan is done by acquiring a cross-sectional plane which is scanned either by using a mechanically moved transducer or by using an electronic multielement probe whereby this cross-sectional plane is moved simultaneously in a direction more or less orthogonal to the cross-sectional plane. This method allows to reconstruct the echo-information in planes which are arbitrarily positioned inside the scanned volume and which are no longer related to the cross-sectional planes used during data acquisition. That means it allows to produce images which cannot be achieved by standard ultrasound scanning due to anatomical reasons. Different visualization algorithms are able to reconstruct echoes from a reflecting surface in a way that the observer has a 3D impression of the object. The viewing angle from which the object is reconstructed is independent from the direction of the ultrasound beams which were used for the data acquisition. Therefore, the observer can xe2x80x9cwalkxe2x80x9d virtually around the object and observe the images from the reconstructed object from different viewing angles on a display. Even for this standard method, a critical issue is the removal of unwanted echoes in front of the object which interfere with the reconstruction of the object of interest. We can find a typical scenario in obstetric applications when the fetus should be examined by abdominal scanning. In that case, there is maternal tissue between the probe and the fetus which covers the face and body of the fetus. Up to now, a simply shaped region of interest (e.g. cube) is selected which contains mainly the object but still some interfering or unwanted information. This described method contains no further information concerning the actual surface of the object and needs also some skills to select the region of interest in a proper way. Additionally, the characteristic of the surface can be important for the examination of the object of interest, such as the perfusion of a tissue on the surface of a tumor or the structure of the vessel which penetrate the tumor.
The present invention improves the method described above with the aim to significantly simplify the user interaction necessary for the representation of an object or the representation of a certain layer within the volume of interest and furthermore to allow to characterize the surface of an object of interest (e.g. perfusion).
This aim is accomplished in that, based on the method described above, a shell is determined which corresponds to a surface or a layer of the object of interest, and only echo information inside this geometrically defined region is used for further processing.
The detection of the surface can be done in an automated way when the echoes coming from this surface are well defined. But also a semi-automated method is possible that means that the contour is edited manually to correct the contours so that it matches the surface in the best way. Finally, the surface is defined by the points of the surface, which are found in the contouring process, by a xe2x80x9cwire-modelxe2x80x9d which connects the points and an interpolation procedure which defines all parts of the surface in between. This defines the object xe2x80x9cshellxe2x80x9d of the present invention. It is possible to eliminate for the processing all echoes which are outside the shell, so the result is a clear view to the object of interest. The main intention of the present invention is to characterize the surface of an object beside the standard 3D representation of the object.
According to a further feature of the present invention, the thickness of the shell can be varied between approximately xe2x80x9czeroxe2x80x9d and a thickness which comprises the complete size of the object. In this way, information coming only from the surface or further information from the object can be processed, which can be displayed for example in reconstructed cross-sectional planes containing only data which are defined by the shell. The selection of shells with different thickness or the continuous variation of the thickness results in additional informationxe2x80x94e.g. if Doppler signals are processedxe2x80x94regarding the perfusion or the structure of the blood flow. Another possibility is that a certain thickness is chosen andxe2x80x94for convex objects by diminishing the diameter of the shellxe2x80x94the object is examined layer by layer.
According to another feature of the present invention, a histogram is calculated from the selected informationxe2x80x94data which correspond either to amplitude or to flow information or to other parameters which can be derived from the ultrasound signal.
The resulting images can be displayed individually. A good choice e.g. is for the first overview a transparent 3D representation. Another option of the present invention is also to display simultaneously a variety of images as e.g. a 3D image combined with a histogram of the flow distribution on the surface of the object whereby the surface is superimposed to the 3D image so that the complex spatial relationship can be visualized.
To document a result or to give an overview, the information in a shell can also be projected/unwound into a plane display by using algorithms which are used for maps.
Further details and advantages of the present invention can be found in the drawings which are described below. The drawings describe a preferred embodiment of the present invention.